Isolation and molecular structures of novel organotellurium(iv) halides, oxyhalide and mixed halide

Article abstract of DOI:10.1039/c2dt30645j

The formation of chiral (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(iv) trihalides (trichloride (5), tribromide (6) and triiodide (7)) and (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(ii) bromide (8) is described. The molecular structure of the first c

Full text of DOI:10.1039/c2dt30645j

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PAPER
Isolation and molecular structures of novel organotellurium(IV) halides,
oxyhalide and mixed halide†
Prakul Rakesh,a Harkesh B. Singh*a and Ray J. Butcherb
Received 21st March 2012, Accepted 15th June 2012
DOI: 10.1039/c2dt30645j
The formation of chiral (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(IV) trihalides (trichloride (5),
tribromide (6) and triiodide (7)) and (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(II) bromide (8) is
described. The molecular structure of the first chiral organotellurium(IV) triiodide (7) is discussed. The
most interesting feature of the structure of 5 is the observation of the shortest intramolecular Te⋯N
distance for any organotellurium(IV) trichloride. Compounds 5 and 6 do not undergo electrophilic addition
reaction with olefins. Attempted addition reaction of 6 with olefin in methanol leads to the isolation of the
rare partially hydrolysed tellurium(IV) halide, methyl-2-(dibromooxotellurium)benzoate (9). Novel stable
mixed halide 12 was isolated from the bromination of 11. DFT calculations indicate that both the isomers
12a and 12b have similar stability.
Introduction
One of the common approaches to introduce tellurium in organic
compounds is the electrophilic addition of organotellurium
halides (RTe(IV)X3 and RTe(II)X where X = Cl, Br, I) to olefins.
The electrophilic addition of organotellurium(IV) trihalides to
olefin was first reported by Campos and Petragnani in the early
1960s.1 The addition of organotellurium halides (1) to olefins is
stereospecific i.e. trans involving a cyclic telluronium ion 2 as
an intermediate (Scheme 1).2 The regioselectivity of addition
reactions is dependent on the polarity of the solvents employed.
Scheme 1 Stereospecific addition of organotellurium(IV) trihalides to
The anti and syn addition products are formed in polar and non-
alkene.
polar solvents respectively.3 Comasseto et al. have reported the
synthesis of cyclic ethers having an aryldihalotelluro group in
We are currently interested in the synthesis of optically active
organotellurium compounds stabilized by intramolecular inter-
action and exploring their application in organic reactions. To our
the β-position4 and tellurolactones5 by the reaction of unsaturated
alcohols and β,γ-unsaturated carboxylic acids respectively with
4-methoxyphenyltellurium(IV) trihalides. Stefani and coworkers
knowledge, the addition reaction of chiral organotellurium(IV) tri-
successfully synthesized vinylic tellurides by the addition of
halides has not been studied. In this paper, we describe the syn-
phenyltellurium(IV) trihalides to terminal acetylenes.6 Recently,
thesis of chiral (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(IV)
trihalides (trichloride, tribromide and triiodide) and (R)-[2-(4-ethyl-
Torubaev et al. have reported the regio- and stereospecific
addition of phenyltellurium(IV) tribromides to ferrocenylacety-
2-oxazolinyl)phenyl]tellurium(II) bromide, and report on their
lene.7 The authors observe that the structure of the product does
efficiency towards addition reaction with double bonds. We also
not depend on the polarity of the solvents used. This is in con-
report, in this paper, the isolation of a rare partially hydrolyzed tri-
trast to the earlier reports.3
bromide derivative, methyl-2-(dibromooxotellurium)benzoate and
the first example of a structurally characterized stable mixed halide,
[2-(dimethylaminomethyl)phenyl]tellurium(IV) dibromide chloride.
aDepartment of Chemistry, Indian Institute of Technology Bombay,
Powai, Mumbai 400 076, India. E-mail: chhbsia@chem.iitb.ac.in;
Fax: +022 2576 7152; Tel: +022 2576 7190
bDepartment of Chemistry, Howard University, Washington D.C., 20059,
USA
Results and discussion
†Electronic supplementary information (ESI) available: The spectro-
scopic data (1H, 13C, 125Te NMR spectra, CHN analysis, ESI-Mass
spectra and FT-IR spectra) for all the compounds (5–9 and 12). CCDC
835165–835169 and 835171. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2dt30645j
Synthesis
The synthesis of chiral (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]-
tellurium(IV) trihalides (trichloride (5), tribromide (6) and
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Scheme 2 Synthesis of (R)-[2-(4-ethyl-2-oxazolinyl)phenyl] tellurium(IV)
trihalides (trichloride, tribromide and triiodide) and (R)-[2-(4-ethyl-2-
oxazolinyl)phenyl]tellurium(IV) bromide.
triiodide (7)) and (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(II)
bromide (8) is depicted in Scheme 2. (R),(R)-Bis[2-(4-ethyl-
2-oxazolinyl)phenyl]ditelluride (4) was synthesized by follow-
ing the literature method.8 The reaction of 4 with an excess of
SO2Cl2 gave compound 5. Similarly, the reaction of 4 with an
excess of Br2/I2 afforded 6 and 7 respectively. Compounds 5, 6,
and 7 are quite stable in air and moisture. Attempts to synthesize
the corresponding RTe(II) X, (X = Cl, Br, I) derivatives by the
stoichiometric control of the halogenating agents were unsuc-
cessful. When 4 was treated with only one equivalent of SO2Cl2
or Br2, tellurium(IV) derivatives 5/6 were obtained instead of the
desired mono halo-derivatives. In the case of I2, a brownish
liquid was obtained. However, compound 8 could be easily syn-
thesized from the reduction of 6 with hydrazine monohydrate in
an ethanolic solution.
Scheme 3 Plausible mechanism for the formation of 9.
In our case, compound 9 is stabilized by an Te⋯O intramolecu-
lar coordination.
The formation of compound 9 may proceed in two steps
(Scheme 3). The initial step involves the nucleophilic substi-
tution of one Br atom, trans to N⋯Te, with traces of H2O
present in methanol. This is followed by the condensation of two
hydrolysed units giving 9 as the exclusive product. The for-
mation of hydrobromic acid during the reaction leads to the
hydrolysis of oxazoline group into an ester group (9). To prove
formation of the proposed protonated oxazoline intermediate in
1
the reaction mixture, H NMR titration experiment was carried
out. The addition of a few drops of the dilute HCl to a solution
of 6 in CDCl3 led to the appearance of a major broad peak at
7.94 ppm. The broad peak is probably due to the overlap of
1H signals of the desired protonated species alongwith the oxo-
tellurium compounds formed. To further confirm the presence of
the protonated species, a D2O exchange study was carried out.
The addition of D2O to the reaction mixture in the NMR tube
led to a significant decrease in the intensity of the peak at
7.94 ppm, thus confirming the presence of the protonated
species. In addition, simple protonated oxazolines are reported in
literature.11 The authors have observed the protonated N–H
1H signal at 10.6 ppm. To avoid the possibility of the overlap of
signals due to in situ formed oxotellurium compounds during
the titration experiments, 4,4-dimethyl-2-phenyl-2-oxazoline was
used in the place of 6. The addition of dil HCl resulted in
appearance of a broad peak at 7.94 ppm. The peak disappeared
on addition of D2O. This unambiguously confirms the formation
of the protonated oxazoline moiety during the protonation reac-
tion. Finally, the hydrolysed species is esterified with the solvent
methanol to give 9. The methanolysis of oxazolines under acidic
conditions is well known.12
The addition reactions of organotellurium electrophiles (5, 6)
with substituted alkenes were attempted. Compounds 5 and 6
were refluxed with cyclohexene in chloroform for 24 hours and
the electrophiles 5 and 6 were found to be unreactive towards the
addition reactions. The change of reaction conditions by varying
solvents, alkene or temperature was ineffective and the reaction
always led to the isolation of the starting materials. The addition
reactions were also attempted using activated electrophile (e.g.
silver triflate derivatives of 5/6) and activated alkene (e.g. nor-
bornene). However, in no case the desired products could be
obtained. Interestingly, when the reaction of 6 with cyclohexene
was carried out under refluxing methanol for 5 hours, a partially
hydrolyzed derivative, methyl-2-(dibromooxotellurium)benzoate
(9) was isolated instead of the addition product. In order to
probe the role of olefin in the hydrolysis reaction, when 6 was
refluxed in methanol without any olefin, the hydrolyzed product
9 was obtained in 65% yield. Beckmann et al. have reported the
molecular structure of a related supermesityltellurium hydroxide
dichloride (RTeCl2(OH); R = 2,4,6-t-BuC6H2).9 The compound
was obtained during the crystallization of supermesityltellurium
(IV) trichloride and its subsequent exposure to moist air. Misra
et al. have also isolated a related monomeric hydroxohalide,
1-C10H7TeCl2OH, by hydrolysis of the corresponding trichlo-
ride. The compound has been isolated as 1 : 1 adduct of
1-C10H7TeCl2OH and 2-pyrrolidinone.10 The isolation of super-
mesityltellurium hydroxide was possible due to the use of the
bulky ligand and 1-C10H7TeCl2OH was stabilized by hydrogen
bonding of the hydroxohalide with cocrystallised 2-pyrrolidinone.
The poor reactivity of the intramolecularly coordinated tellur-
ium trihalides in the reactions described in the preceding section
is most probably due to the high stability of the trihalides having
a strong Te⋯N (sp2) interaction.13 It is well known that the
Te⋯N (sp3) intramolecular interaction is weaker than the Te⋯N (sp2)
interaction.8,13 In view of this we envisaged to investigate the
reactions of tellurium trihalides having a sp3 nitrogen atom as the
10708 | Dalton Trans., 2012, 41, 10707–10714
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Fig. 1 Position isomers of 12.
Scheme 4 Synthesis of [2-(dimethylaminomethyl)phenyltellurium(IV)
dibromide chloride (12).
donor atom. The reactivity of [2-(dimethylaminomethyl)phenyl]-
tellurium(IV) tribromide,14 having Te⋯N (sp3) secondary inter-
action, was attempted towards substituted alkenes. However
[2-(dimethylaminomethyl)phenyl]tellurium(IV) tribromide also
did not undergo addition reaction on alkenes. To confirm that the
Te⋯N interaction is responsible for the poor reactivity of the tri-
halide, the protonation of the nitrogen of 10 was attempted
(Scheme 4). This would have yielded a coordination free tellur-
ium trihalides for investigation of the reactivity towards alkenes.
However, the attempted protonation, yielded [2-(dimethylamino-
methyl)phenyl]tellurium(II) chloride (11).15,16 Compound (11)
was further derivatized by addition of Br2 to afford a novel
mixed halide [2-(dimethylaminomethyl)phenyl]tellurium(IV)
dibromide chloride (12). There are very few reports in the litera-
ture on mixed halide17 and in no case the mixed halides has
been isolated and characterized successfully. Compound 12
could be successfully isolated and characterized only due to
strong intramolecular interaction between N and Te.
Fig. 2 The expansion of the alkyl region of the 1H NMR spectra of 12
at (a) 400 MHz (b) 500 MHz (c) 700 MHz.
1
The H NMR and 13C NMR spectra were quite similar for
5–8. The 125Te NMR chemical shifts of compounds (5–7) are in
the range expected for organotellurium(IV) halides i.e.
1100–1200 ppm.13 The 125Te NMR chemical shift of compound
8 (1199) is downfield shifted compared to compound 6 (1129 δ).
The difference in the chemical shift is probably due to better
delocalization of the lone pair in 8 in comparison to 6. This
results in more aromatic character in the five-membered ring
having N and Te intramolecular interaction in compound 8
than 6.
process, a low variable temperature NMR study was attempted
in DMSO-d6. However, the low temperature variable H NMR
study of 12 was not successful in DMSO-d6 due to the high
1
freezing point of DMSO-d6 (18.5 °C). To overcome this
1
problem, the H NMR spectra of 12 were recorded at 400, 500
and 700 MHz at room temperature. The presence of more than
1
six species was clearly observed from the H NMR spectrum of
12 at 700 MHz at room temperature as shown in Fig. 2.
The molecular structure of 5 is shown in Fig. 3. The coordi-
nation geometry around the Te atom can be considered as dis-
torted pseudo-octahedral in which N, Cl3, C11 and the lone
pair are nearly planar and Cl1 and Cl2 atoms are trans to each
other. The intramolecular Te⋯N distance (2.2414(18) Å) is even
shorter than that observed in [2-[1-(3,5-dimethylphenyl)-
2-naphthyl]-4,5-dihydro-4,4-methyloxazole]tellurium(IV) chloride
(2.251(3) Å).13 This is the shortest bond (Te⋯N) among all
other reported organotellurium(IV) trichloride.20 As a conse-
quence the trans bond Te–Cl3 (2.4871(6) Å) is longer than the
Te–Cl distance (2.451(12) Å) observed in [2-[1-(3,5-dimethyl-
phenyl)-2-naphthyl]-4,5-dihydro-4,4-methyloxazole]tellurium(IV)
chloride.13 The molecular structure of 6 is quite similar to that
observed for compound 5 (Fig. 4). The Te⋯N1 bond distance
(2.263(5) Å) is close to Te–N single bond covalent radii
(2.07 Å), however, it is longer than the Te⋯N interaction
(2.244 Å) in 2-(2-pyridyl)phenyltellurium(IV) tribromide21 and
shorter than the Te⋯N (2.422(5) Å) in [2-(dimethylamino-
methyl)phenyl]tellurium(IV) tribromide.14 Molecule 7 is the first
chiral organotellurium(IV) triiodide to be structurally character-
ized. The geometry around the Te atom is similar to that
observed for compounds 5 and 6 (Fig. 5). The Te⋯N distance
(2.284(2) Å) is longer than the sum of Te and N single bond
covalent radii (2.07 Å) and the Te–I3 distance (2.8435(2) Å) is
1
The formation of 9 was initially indicated by H NMR, 13C
1
NMR, 125Te NMR, FT-IR spectroscopy. The H NMR spectrum
shows the absence of the oxazoline group and presence of
–OCH3 peak at 4.24 δ. The signal at 174.21 δ shows the pres-
ence of a CvO peak in the 13C NMR spectrum and a sharp
peak at 1636 cm−1 shows νCvO peak in FT-IR spectrum. The
125Te NMR spectrum signal (1431 δ) is in the range of oxotellur-
1
ium compounds.18 The H NMR spectrum of 12 showed broad
signals for all the protons. Similarly, the 13C NMR spectrum of
12 showed the presence of six isomers. 125Te NMR spectroscopy
is a very sensitive technique and the 125Te NMR spectrum
exhibited six peaks (1385, 1406, 1412, 1419, 1424 and
1426 δ). Since, CHN analysis data matched very well with the
calculated values, it was concluded that the several sets of peaks
in 13C NMR and 125Te NMR were due to the presence of several
isomers/slow exchange process in solution. Also compound 12
is expected to have two positional isomers in which either Cl or
Br will be trans to N (Fig. 1). In addition, as observed
earlier,18,19 the trihalides show presence of several species in
equilibrium with each other in solvent DMSO-d6. Thus, the
number of species observed in DMSO-d6 is both due to the pres-
ence of positional isomers and solvent DMSO coordinated
species in the NMR tube. In order to probe the exchange
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Fig. 3 Molecular structure of 5 and selected bond lengths (Å) and
angles (°). Hydrogen atoms are omitted for clarity. Cl1–Te 2.5139(7),
Cl2–Te 2.4789(7), Cl3–Te 2.4871(6), Te–C1 2.125(2), Te–N 2.2414(18);
C1–Te–N 76.61(8), N–Te–Cl3 168.55(5), Cl1–Te–Cl2 168.81(2).
Fig. 5 Molecular structure of 7 and selected bond lengths (Å) and
angles (°). Hydrogen atoms are omitted for clarity. Te–N 2.284(2), Te–I3
2.8435(2); I3–Te–N 169.50(6), I2–Te–I3 94.713(8), I2–Te–I1 161.208(8).
Fig. 4 Molecular structure of 6 and selected bond lengths (Å) and
angles (°). Hydrogen atoms are omitted for clarity. Te–N1 2.263(5),
Te–Br2 2.6314(8); C1–Te–N1 76.0(2), N1–Te–Br2 168.03(13), Br3–Te–
Br1 161.20(3).
Fig. 6 Molecular structure of 8 and selected bond lengths (Å) and
angles (°). Hydrogen atoms are omitted for clarity. Te–C1 2.1113(10),
Te–N 2.204(8), Te–Br 2.723(14); N–Te–Br 167.58(20), C1–Te–Br
75.86(21), C1–Te–N 91.72(25).
slightly longer than the sum of Pauling’s covalent radii22 of
Te (1.37 Å) and I (1.39 Å). The packing diagram of 5 shows a
chain-like structure due to weak intermolecular interaction
between Te and equatorial Cl3 (3.616 Å).
The geometry around Te atom in 8 is T-shaped with the tellur-
ium atom bonded to axial bromine, nitrogen atom and the equa-
torial aromatic carbon atom (Fig. 6). The Te⋯N distance
(2.204(8) Å) is shorter than the corresponding distance in [2-[1-
(3,5-dimethylphenyl)-2-naphthyl]-4,5-dihydro-4,4-methyloxazole]-
tellurium(II) bromide((2.2520(4) Å)14 and phenylazophenyl-
(C, N′)tellurium(II) bromide (2.219(8) Å).23 The <N–Te–Br
(167.58(20)°) is close to linear. Compound 8 exists as a dimer
due to weak secondary Te⋯Br (3.899 Å) interaction.
The Flack parameter (Table 1) of chiral compounds 5–8 is
close to zero, confirming the optical purity of the halides. Appli-
cation of Cahn, Ingold and Prelog rule24 confirms the presence
of (R)-enantiomorph in the case of all chiral compounds (5–8).
The optical rotation of compounds 5–8 are mentioned in the
Experimental section.
The crystals of 9 for single X ray crystallography were
obtained at room temperature from CHCl3–hexane mixture
(2 : 1). Compound 9 crystallizes in monoclinic crystal system
with P21/c space group. The geometry around oxygen is
V-shaped with Te1–O–Te2 bond angle of 125.9(4) (Fig. 7). This
bond angle is similar to that observed for bis[(2-(phenylazo)-
phenyl-C,N′)tellurium] oxide (122.9(15)).18 The Te–O bond
lengths Te1–O and Te2–O bond lengths are 1.963(8) and
1.951(8) Å respectively and are close to those reported for bis-
[(2-(phenylazo)phenyl-C,N′)tellurium]
oxide
(2.026(3);
2.007(3) Å). The values for these Te–O bond lengths are close to
the sum of the covalent radii for tellurium and oxygen
(Te, 1.35 Å; O, 0.73 Å) suggesting their single bond character.22
The geometry around tellurium atom (Te1) is pseudo-octahedral
in which O2A, C1A, O and lone pair are planar and two Br are
trans to each other. The intramolecular distance of Te1⋯O2A
(2.501(9) Å) is much shorter than sum of the van der Waals radii
for tellurium and oxygen (Te, 2.06 Å; O, 1.52 Å)26 and longer
than the sum of the covalent radii for tellurium and oxygen
(Te, 1.35 Å; O, 0.73 Å).22 The bond (Te1–O) (1.963(8) Å) trans
to Te1⋯O2A is similar to the Te–O distance in trans-super-
mesityltellurium hydroxide dichloride (1.993(2) Å)9 and bis[2-
(dimethylaminomethyl)phenyl]hydroxytelluronium
cation
(1.961(16) Å).25 The bond angle of O2A–Te1–O (162.3(3)) is
deviated from 180° due to presence of lone pair. The sum of van
der Waals radii of Te and Br (3.91 Å)26 is longer than secondary
interaction between Te⋯Br (3.731 Å) to form a dimer.
10710 | Dalton Trans., 2012, 41, 10707–10714
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Table 1 Crystal data and structure refinement for 5–8
Compounds
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
5
6
7
8
C11H12Cl3NOTe
408.17
Orthorhombic
P212121
8.8565(2)
12.1571(3)
13.2983(3)
90
C11H12Br3NOTe
541.55
Orthorhombic
P212121
7.5355(3)
12.8672(4)
15.3557(5)
90
C11H12I3NOTe
682.52
Orthorhombic
P212121
7.791(10)
13.6338(2)
15.5148(2)
90
C11H12BrTeNO
380.72
Monoclinic
I12/m1
11.6722(3)
6.9965(2)
15.7268(5)
90
β (°)
90
90
90
90
90
90
106.463(3)
90
1231.67(6)
4
2.053
5.633
γ (°)
V (Å3)
1431.82(6)
4
1.893
2.620
9905
0.0264
0.0484
5448/0/155
0.010(14)
0.967
1488.90(9)
4
2.416
10.033
23 521
0.0582
0.0964
6047/0/155
0.018(13)
1.041
1648.00(4)
4
2.751
Z
D(calcd) Mg m−3
abs coeff (mm−1
)
7.412
Reflens collected
34 752
0.0248
0.0447
8380/0/155
0.00(2)
1.019
10 227
Final R(F) [I > 2σ(I)]a
wR(F2) indices [I > 2σ]
No. of data/restrains/params
Absolute structure params
Goodness of fit on F2
0.0568
0.1366
2723/0/94
1.212
2
2 2
2 2
a Definitions: R(Fo)) = ∑ ||Fo − jFc||/∑| Fo| and wR(Fo ) = {∑[w(Fo2 − Fc ) ]/∑[w(Fc ) }1/2
.
Fig. 7 Molecular structure of 9 and selected bond lengths (Å) and
angles (°). H atoms are omitted for clarity. Te1–C1A 2.126(12), Te1–Br11
2.619(16), Te1–Br12 2.708(16), O2A–Te1 2.501(9), Te1–O 1.963(8);
O2A–Te1–Br11 88.3(2), O2A–Te1–Br12 93.0(2), C1A–Te1–Br11
86.60(3), C1A–Te–Br12 86.60(3), O–Te1–Br11 88.1(2), O–Te1–Br12
88.5(3), O2A–Te1–O 162.3(3), C1A–Te1–O 89.0(4).
Fig. 8 Molecular structures of 12a, 12b and selected bond lengths (Å)
and angles (°). Hydrogen atoms are omitted for clarity. For compound
12a: Te1–N1 2.4315(11), Te1–Cl1 2.44(1), Te1–Br1 2.730(2), Te1–Br2
2.647(2); Cl1–Te1–N1 161.6(2), N1–Te1–Br2 89.1(13), Br2–Te–Br1
164.4(3). For compound 12b: Te1–N1 2.421(5), Te1–Cl1 2.601(1), Te1–
Br1 2.640(2), Te1–Br2 2.60(2); Cl1–Te1–N1 92.6(2), N1–Te1–Br2
160.9.1(13), Br2–Te–Br1 89.4(3).
Two types of crystals (12a and 12b), having slightly different
morphology, were formed during the recrystallization of 12 from
CHCl3. The crystals of compound 12 were manually separated.
The crystal structure determined at room temperature (22 °C)
was compound 12a. However, the crystal structure determined at
low temperature (−150 °C) was 12b. The R factor of 12a (8.1) is
higher than the R factor of 12b (3.8). Compound 12a crystallizes
in monoclinic crystal system with P21/c space group. The mole-
cular unit of 12a is shown in Fig. 8. The chlorine atom is trans
to nitrogen. The highest occupancy of Br : Cl is 2.37 : 0.63. The
coordination geometry around the Te1 atom can be considered as
distorted pseudo-octahedral in which N1, Cl1, C1 and the lone
pair are planar and two Br atoms are trans to each other. The
intramolecular Te1⋯N1 distance (2.4315(11) Å) is similar to
Te⋯N (2.442(5) Å) bond distance in [2-(dimethylaminomethyl)-
phenyl]tellurium(IV) tribromide.14 The bond distance of Te–Cl1
(2.44(1) Å) is similar to the bond distance of trans Te–Cl in
[8-(dimethylamino)-1-naphthyl]tellurium(IV) trichloride (2.442
(2) Å).27 A dimer was formed due to a weak Te1⋯Br1B
(3.649 Å) and Te2⋯Br1A (3.548 Å) intermolecular interactions
(Fig. 9).
Fig. 8 also shows the pictorial diagram of 12b obtained from
single X-ray crystallography at low temperature (−150 °C). The
molecular structure is similar to 12a. The only difference is that
the chlorine atom is trans to nitrogen. The highest occupancy of
Br : Cl is 2.04 : 0.96. The Te1–Cl1 bond distance (2.601(5) Å) is
larger than the bond distance in 12a (2.44(1) Å). This is due to
the involvement of Cl1 atom in dimer formation by the weak
interaction (3.414 Å) between Te and Cl1 (Fig. 9). As evident
from the R value and Br : Cl ratio at 22 °C and −150 °C, the
exchange process is slow at low temperature and results is lower
R value and Br : Cl ratio is close to expected ratio.
In order to check that which isomer was the lower energy
isomer, the geometries of 12a, and 12b were optimized.
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reaction was carried out in a similar manner to that described
above for the synthesis of 5 to obtain a yellow precipitate. The
compound was recrystallized from CHCl3–hexane (1 : 4) mixture
to give yellow crystals of 6: Yield 0.71 g, 79.7%, mp
159–161 °C. Anal. Calcd for C11H12Br3NOTe: C, 24.40; N,
2.59; H, 2.23. Found C, 24.9; N, 3.16; H, 2.00. 1H NMR
(CDCl3): δ 1.18 (t, 3H), 1.94–2.09 (m, 2H), 4.64–4.77 (m, 2H),
5.16 (m, 1H), 7.74 (m, 1H), 7.96 (m, 2H), 8.82 (d, 1H). 13C
NMR (CDCl3): δ 11.08, 27.96, 65.31, 78.20, 121.71, 129.30,
130.03, 131.81, 136.72, 146.15, 162.68. 125Te NMR (CDCl3):
δ 1129. ES-MS: (m/z) 284 (PhTeBr+). IR (KBr, cm−1): 1625.7
(νCvN). [α]2D1 = −14.4(c = 0.26%, CHCl3).
Fig. 9 Dimer of 12a and 12b.
Geometries were fully optimized at the b3pw91 level of theory
with the use of the lanl2dz basis sets.28 The difference between
the energies of 12a and 12b is only 0.09 kcal mol−1. It shows a
similar stability for compounds 12a and 12b. The computed geo-
metry of 12a and 12b were in well conformity with the crystal
geometry.
(R)-[2-(4-Ethyl-2-oxazolinyl)phenyl]tellurium(IV) triiodide (7)
To a stirred solution of 4 (0.3 g, 0.49 mmol) in dry CCl4 (20 ml)
was added a solution of I2 (0.378 g, 1.47 mmol) and the reaction
was carried out in a similar manner to that described above for
the synthesis of 5 to obtain a brown precipitate. The compound
was recrystallized from CHCl3–hexane (1 : 4) mixture to give
brown crystals of 7: Yield 0.38 g, 56% mp 144–146 °C. Anal.
Calcd for C11H12I3NOTe: C, 19.36; N, 2.05; H, 1.77. Found C,
19.88; N, 2.03; H, 1.60. 1H NMR (CDCl3): δ 1.16 (t, 3H),
1.92–2.07 (m, 2H), 4.57–4.72 (m, 2H), 5.06 (m, 1H), 7.82
(m, 3H), 8.71 (m, 1H). 125Te NMR (CDCl3): δ 1097 ES-MS:
(m/z) 303 [(C11H12NOTe)+, 79]. 13C NMR (CDCl3): δ 11.45,
28.22, 65.67, 77.60, 122.32, 129.32, 131.42, 132.50, 134.90,
136.20, 169.95. IR (KBr, cm−1): 1626 (νCvN). [α]D19 = −46.2
(c = 0.083%, CHCl3).
Experimental section
All reactions were carried out under N2 atmosphere. Solvents
were purified and dried by standard techniques.29 (R),(R)-Bis-
[2-(4-ethyl-2-oxazolinyl)phenyl]ditelluride (4) and [2-(dimethyl-
aminomethyl)phenyl]tellurium(II) chloride (11) were prepared by
literature method.8,15 Melting points were recorded in capillary
tubes and are uncorrected. H and 13C spectra were obtained at
1
399.88 and 100.56 MHz respectively in CDCl3 on a Varian
VXR 400 S spectrometer. 125Te NMR spectra were recorded at
94.75 MHz in CDCl3 on a Varian VXR 300 S spectrometer.
Chemical shifts are cited with respect to SiMe4 as internal
(1H and 13C) and Me2Te as external standard. Elemental analysis
was performed on a Carlo-Erba model 1106 CHNS elemental
analyzer. Infrared spectra were recorded in the range
4000–400 cm−1 on a Nicolet Impact 400 FT-IR spectrometer.
ES-MS spectra were recorded at room temperature on a Q–Tof
(YA-105) micromass spectrometer. Specific optical rotations
were measured on AUTOPOL IV digital polarimeter.
(R)-[2-(4-Ethyl-2-oxazolinyl)phenyl]tellurium(II) bromide (8)
A stirred solution of compound (6) (0.3 g, 0.55 mmol) in dry
ethanol (15 ml) was treated drop-wise with NH2NH2·H2O
(0.027 ml, 0.55 mmol) in dry ethanol (10 ml) under N2 at room
temperature. After addition, the reaction mixture was refluxed for
2 hours. Then it was concentrated and the resulting yellow solid
was recrystallized from CHCl3–hexane (1 : 4) mixture to give
pale yellow crystals of 8: Yield 0.12 g, 57%, mp 132–134 °C.
Anal. Calcd for C11H12BrNOTe: C, 34.61; N, 3.67; H, 3.16.
(R)-[2-(4-Ethyl-2-oxazolinyl)phenyl]tellurium(IV) trichloride (5)
A stirred solution of (R),(R)-bis[2-(4-ethyl-2-oxazolinyl)phenyl]-
ditelluride (4) (0.3 g, 0.49 mmol) in dry CCl4 was treated with
SO2Cl2 (0.12 ml, 1.47 mmol) under N2 at room temperature.
The reaction mixture was stirred for further 2 hours and then
filtered to give a white precipitate. The compound was recrystal-
lized from CHCl3–hexane (1 : 4) mixture to give white crystals
of 5: Yield 0.33 g, 82%, m.p 126–128 °C. Anal. Calcd for
C11H12Cl3NOTe: C, 32.37; N, 3.43; H, 2.96. Found C, 32.29; N,
3.80; H, 2.96. 1H NMR (CDCl3): δ 1.18 (t, 3H), 1.90–2.04
(m, 2H), 4.61–4.68 (m, 2H), 5.12 (m, 1H), 7.7 (m, 1H), 7.94
(m, 2H), 8.75 (m, 1H). 13C NMR (CDCl3): δ 10.77, 27.89,
64.99, 78.39, 121.63, 128.12, 129.18, 131.68, 136.78, 152.85,
163.78. 125Te NMR (CDCl3): δ 1115. ES-MS: (m/z) 303
[(C11H12NOTe)+]. IR (KBr, cm−1): 1610 (νCvN). [α]1D9 = 35.7
(c = 0.18%, CHCl3).
1
Found C, 34.68; N, 4.22; H, 2.96. H NMR (CDCl3): δ 1.12 (t,
3H), 1.84 (m, 2H), 4.54 (m, 2H), 4.96 (t, 1H), 7.43 (t, 1H), 7.56
(t, 1H), 7.87 (d, 1H), 8.65(d, 1H). 13C NMR (CDCl3): δ 9.19,
27.25, 63.58, 76.99, 122.56, 127.11, 128.49, 132.66, 133.49,
135.32, 168.73. 125Te NMR (CDCl3): δ 1199. ES-MS: (m/z) 303
[(C11H12NOTe)+]. IR (KBr, cm−1): 1608 (νCvN). [α]1D9 = −35
(c = 0.16%, CHCl3).
Methyl-2-(dibromooxotellurium)benzoate (9)
The yellowish solid (0.3 g) (6) was added in a 10 ml methanol
solution. After 3 hours of reflux, the solid was dissolved comple-
tely. The light yellow solution was reduced and the resulting
light yellow solid was recrystallized by hexane and chloroform
(2 : 1) mixture to give white crystals. Yield 0.15 g, 65% mp
212–214 °C. Anal. Calcd for C16H14Br4O5Te2: C, 22.32; H,
1.64. Found C, 22.43; H, 1.70. 1H NMR (CDCl3): δ 4.24
(s, 3H), 7.71 (t, 1H), 8.05 (t, 1H), 8.16 (d, 1H), 8.81
(R)-[2-(4-Ethyl-2-oxazolinyl)phenyl]tellurium(IV) tribromide (6)
To a stirred solution of 1 (0.5 g, 0.82 mmol) in dry CCl4 (20 ml)
was added a solution of Br2 (0.126 ml, 2.4 mmol) and the
10712 | Dalton Trans., 2012, 41, 10707–10714
This journal is © The Royal Society of Chemistry 2012

View Article Online
Table 2 Crystal data and structure refinement for 9, 12a and 12b
Compounds
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
9
12a
12b
C16H14Br4O5Te2
861.11
C9H12Br2ClNTe
457.07
Monoclinic
P21/c
14.7827(8)
12.0157(5)
15.8651(7)
90
C9H12Br2ClNTe
458.18
Monoclinic
P21/c
7.2854(3)
12.4785(5)
14.4098(6)
90
Monoclinic
P121/c1
14.8602(11)
17.5288(8)
8.9476(5)
90
β (°)
102.740(7)
90
2273.3(2)
4
2.516
9.620
109.130(5)
90
2662.41(2)
8
2.363
26.859
98.200(4)
90
1296.61(9)
4
2.347
8.700
γ (°)
V (Å3)
Z
D(calcd) (mg m−3
)
Abs coeff (mm−1
)
Reflens collected
15 286
0.0977
0.1767
7284/12/246
1.048
9770
0.0928
0.2428
5118/12/281
1.015
8229
Final R(F) [I > 2σ(I)]a
wR(F2) indices [I > 2σ]
No. of data/restrains/params
Goodness of fit on F2
0.0380
0.0491
4241/1/141
0.956
2
2 2
2 2
a Definitions: R(Fo)) = ∑||Fo − jFc||/∑|Fo| and wR(Fo ) = {∑[w(Fo2 − Fc ) ]/∑[w(Fc ) }1/2
.
(d, 1H).13C NMR (CDCl3): δ 55.79, 126.25, 130.76, 130.89,
131.44, 137.58, 150.51, 174.21. 125Te NMR (CDCl3): δ 1431.
ES-MS: (m/z) 249.9 [(C7H4O2Te, M+)], 264.9 [(C8H7O2Te)+,
60]. IR (KBr, cm−1): 1636 (νCvO), 701 (νTe–O).
DMSO-d6): δ 1385, 1406, 1412, 1419, 1424, 1426. ES-MS:
(m/z) 234 [(C8H9Te)+, 30%], 264 [(C9H12NTe)+, 20%].
X-ray crystallographic study
The diffraction measurements for compounds 5–8, 9, 12a and
12b were performed on a Oxford Diffraction Gemini diffract-
ometer using graphite-monochromated Mo Kα radiation (λ =
0.7107 Å). The structures were solved by routine heavy-atom
using SHELXS 9730 and Fourier methods and refined by full-
matrix least squares with the non-hydrogen atoms anisotropic
and hydrogens with fixed isotropic thermal parameters of
0.07 Å2 using the SHELXL 97 program.31 The hydrogens were
partially located from difference electron-density maps, and the
rest were fixed at calculated positions. Scattering factors were
from common sources.32 Some details of data collection and
refinement are given in Tables 1 and 2.
General procedure for the addition reaction of alkene with
tribromide
A stirred solution of compound (4) (0.6 g, 0.1 mmol) in dry
MeOH (10 ml) was treated drop-wise with Br2 (0.26 g,
0.33 mmol) in dry MeOH (10 ml) under N2 at 0 °C. Reaction
continued for 2 hours to get yellow precipitate. Cyclopentene
(0.16 g, 0.25 mmol) was added in the reaction mixture. Reaction
mixture was further continued for 24 hours. The reaction mixture
was concentrated to get the solid.
[2-(Dimethylaminomethyl)phenyl]tellurium(II) dibromide
chloride (12)
Conclusions
A stirred solution of [2-(dimethylaminomethyl)phenyl]tellurium(II)
chloride (11) (0.2 g, 0.66 mmol) in dry CHCl3 (10 ml) was
treated with Br2 (0.37 ml, 2.34 mmol) under N2 at 0 °C. The
reaction mixture was stirred for further 2 hours and then reduced
to half volume and kept in a freezer to get a yellow crystalline
solid of 12. Yield 65% mp 200–202 °C. Anal. Calcd for
C9H12Br2ClNTe: C, 24.04; N, 3.47; H, 2.57. Found C, 23.65; N,
3.06; H, 2.65. 1H NMR (400 MHz, DMSO-d6,): δ 3.01–3.03 (m,
6H), 4.51–4.58 (m, 2H), 7.53–7.60 (m, 1H), 7.62–7.67 (m, 2H),
8.37–8.49 (m, 1H). 1H NMR (500 MHz, DMSO-d6,):
δ 2.92–3.04 (m, 6H), 4.49–4.59 (m, 2H), 7.54–7.57 (m, 1H),
7.64–7.68 (m, 2H), 8.39–8.49 (m, 1H). 1H NMR (700 MHz,
DMSO-d6,): δ 2.99–3.11 (m, 6H), 4.57–4.69 (m, 2H), 7.59–7.63
(m, 1H), 7.71–7.76 (m, 2H), 8.46–8.56 (m, 1H). 13C NMR
(400 MHz, DMSO-d6,): δ 47.0, 47.1, 47.3, 47.4, 48.1, 48.2,
48.4, 48.6, 63.8, 63.9, 64.2, 64.2, 64.5, 127.6, 130.0, 130.1,
130.2, 130.3, 130.8, 131.2, 131.7, 132.6, 133.1, 133.5, 139.6,
139.9, 141.6, 143.7, 144.2, 146.2.125Te NMR (400 MHz,
In summary, we have successfully isolated and structurally
characterized a series of chiral tellurium(IV) derivatives, includ-
ing the rare (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(IV)
triiodide (7). Compounds 5 and 6 did not undergo an electrophi-
lic addition reaction on alkenes. The partial hydrolysis of chiral
(R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(IV)
tribromide
results into achiral methyl-2-(dibromooxotellurium)benzoate (9).
Bromination of 11 leads to the formation of novel mixed halide
12. The similar energies of 12a and 12b indicate that both
isomers have similar stability.
Acknowledgements
HBS is grateful to the Department of Science and Technology
(DST), New Delhi-110016 (India), for the Ramanna Fellowship.
PR wishes to thank CSIR for a SRF fellowship.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 10707–10714 | 10713

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10714 | Dalton Trans., 2012, 41, 10707–10714
This journal is © The Royal Society of Chemistry 2012